What size outboards to replace inboard?

Reading more about it I am not sure this “new” 25 Is a true high thrust motor….

If you could find them - a pair of 9.9 high thrust motors would be fabulous.

Finding one will be hard enough.
 
Agreed - 15-20 is fine - just make sure it's a sailpower / high thrust NOT a standard outboard as a standard 15hp will be way too high geared for the use you have which is higher thrust low speed work.
 
Rivers & creeks said:
We’re faced with a dilemma; the right boat has come up for sale, a type we’ve been looking for, for a long time. The inboard petrol engine is knackered and it has an out drive of unknown condition. It’s 26.5 feet, a fair amount of windage but we have a very fixed usage for it: tidal Suffolk river. This boat will never see waves big enough to cause a mirror dinghy problems! Slow and hull speed will be its sole habitat. Hull speed is 6.4 knots so whether we put the right size engines on or bigger ones, the speed through the water will be the same. Still we need enough oomph to manoeuvre so our plan is twin steered outboards to give power, redundancy and added manoeuvrability.
What size do we need for pottering about but still being able to push a high-windage boat and to stop it without it being a liability?

Thank you for any advice you have.
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What boat is it and how do you intend mounting the outboard?
 
Tranona said:
What boat is it and how do you intend mounting the outboard?
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I was going to ask similar .. but assumed OP had ideas already formed.

I have an outdrive boat and looking at it .. the mounting of an outboard instead would not be so easy ...

Blanking of the transom where outdrive mounted .... modifying the steering .... removal of inboard engine ... quite an undertaking. And no doubt expensive.
 
Refueler said:
I was going to ask similar .. but assumed OP had ideas already formed.

I have an outdrive boat and looking at it .. the mounting of an outboard instead would not be so easy ...

Blanking of the transom where outdrive mounted .... modifying the steering .... removal of inboard engine ... quite an undertaking. And no doubt expensive.
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I don’t know how to attach pictures on this forum, I keep getting error messages.

Blanking off the drive is very simple, a classic build-up, fill and fair with resin ply and then a hefty strengthen of the transom via the old engine compartment.

On the outside a combined outboard/swim platform pod that costs £2k and is bolted on.
 
Rivers & creeks said:
I don’t know how to attach pictures on this forum, I keep getting error messages.

Blanking off the drive is very simple, a classic build-up, fill and fair with resin ply and then a hefty strengthen of the transom via the old engine compartment.

On the outside a combined outboard/swim platform pod that costs £2k and is bolted on.
Click to expand...
Need to resize photos down to around 40% before the forum system will accept them.
 
If you have not seen it my thread on a similarish project may be of interest:
dpb

Thread '80's Sea Ray Inboard to Outboard Conversion.'

First off this is not a how to post, infact it may turn out to be a how not to post as the work is under way.
The work is being carried out on my project boat, subject of this thread:

My 80's Sea Ray 197 Monaco Project

The reason for the conversion is as a result of problems with the engine restore related on this thread:

Mercruiser 4.3 V6 rebuild fail.....so next step?

To fix the engine issues was going to cost me in the region of £2000 and I still had a seized up leg to sort out and the boat is unlikely to be worth such further expediture.
At first I considered a change...
  • Like
 
dpb said:
If you have not seen it my thread on a similarish project may be of interest:
dpb

Thread '80's Sea Ray Inboard to Outboard Conversion.'

First off this is not a how to post, infact it may turn out to be a how not to post as the work is under way.
The work is being carried out on my project boat, subject of this thread:

My 80's Sea Ray 197 Monaco Project

The reason for the conversion is as a result of problems with the engine restore related on this thread:

Mercruiser 4.3 V6 rebuild fail.....so next step?

To fix the engine issues was going to cost me in the region of £2000 and I still had a seized up leg to sort out and the boat is unlikely to be worth such further expediture.
At first I considered a change...
  • Like
Click to expand...
Crickey you did an awesome job there; it’s convinced me that it’s not a job for me though!
 
Just get a 15hp and a little 5hp kicker to get you home if the 'big' one conks. It is not as if you are on the high seas .

I used to run a small outboard Mobo from ¨Portugal to Spain each year to clear the registration. OK it had a 75 hp, but a little 5 as last resort.. Owner like doing local stuff, but not confident to do the 'high seas'. Never used the little one.

Two bigger OBs for this use, really is not a great idea.
 
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